From what I have seen, the XC8 doesn't have allot on the 7. In a drag that is. I raced a 2001 ProX 600 and a 2002 XC7 with my 98 XC600, and the 7 would start to pass about 1000 ft. in the snow, never saw the 6. My 98 is stock other than jetting, clutching. It's the little lady's sled.
I think the XCs are good sleds, just have bad calibrations. Even the government got on Polaris's case about the rich jetting, becuase of environmental concerns. Jetting will open them right up.